We have already seen in the previous blog that humans played a huge part in the extinction of megafauna during the Pleistocene. Whilst there is much controversy as to the cause of megafaunal collapse during this period, this blog will review whether man can be solely blamed for the extinction of over 60 faunal species in Australia. Extinctions mainly occured with terrestrial megafauna, leaving marine megafauna untouched (Stuart 1999). Consequently, the Australian megafauna that became extinct 46.4 kyr mostly comprised of large marsupials, birds and reptiles. Humans evolved in Africa, but it is believed that over 85,000 years ago humans left this continent and traveled through the Southern Arabian peninsula towards India. From here, they expanded in all directions with some crossing from Timor into Australia around 65,000 years ago. As a result, there is much debate as to suggest whether the timing of first human colonization and the extinction of mega fauna is a coincidence (Field 2008), or whether man was the cause. Johnson (2006) believes that most if not all of the 68 mega faunal species became extinct at the time of human arrival on the Australian continent, subsequently disappearing within 5000 years. Evidence for the over kill hypothesis is found in the remains of butchered megafauna in Cuddie Springs in New South Wales. Animal remains at the springs dated well after previously though date of extinction, suggesting that protracted overkill was the likely explanation.
Australia suffered the greatest number of losses including 14 of 16 Pleistocene mammalian genera, 6 reptiles and at least 3 birds, including the flightless bird Genyornis newtoni (Murray, 1984, 1991; Koch andBarnosky, 2006). Difficulty in finding the reasons behind such losses are due to the fact people routinely dismember and butcher animals in the process of consumption, and as a consequence of this behavior remains are rarely if ever found (Field et al 2008). Evidence that supports the claim that humans were responsible for mass faunal extinction is found in the demise of animals that were resilient to glacial interglacial cycling. Recently, the identification of some faunal species having adaptations to aridity has been forwarded as evidence that climate change was not a major force driving this process. By default, humans must have been responsible (Field et al 2012). Further evidence includes the disappearance of G.newtoni in central Australia, which coincides with initial human colonization in the region. Man could have caused this disappearance due to hunting practices over long periods, or possibly through habitat fragmentation which would have altered the landscape causing large scale extinctions. Evidence of landscape modification is shown in the increase of charcoal found in fossil records. A study of Tight Eastern Cave in South West Australia showed that charcoal concentration rose immediately after human arrival. This indicates that human induced habitat modification might have caused the extinction of megafauna and not over kill. However whilst the increase of charcoal is evident, fire frequency during the Holocene from c8.5kyr does not bare any relationship to human activities (Field et al 2008). High loss of large browsing herbivores (above 30kg) over smaller grazing herbivores, also reinforces evidence to suggest that over hunting is a likely cause of high extinction rates. Similarly, the fact that there is very little evidence of coexistence between humans and megafauna implies man being responsible for such losses. The suggestion that climate could have been responsible for the decline of mega fauna is undermined by the fact that climate change in this region was relatively ‘mild’.
Overall, reasons for the extinction of mega fauna in Australia are complex. Whilst there is evidence to suggest that the colonization of humans in the region was the primary cause of faunal extinction, there is still lack of supporting evidence. Australia is such a dry continent and ‘stratified sequences are few and far between’ (Field et al 2012). Consequently lack of fossil evidence and poor data sets are fundamental obstacles facing scientists trying to resolve this extinction controversy. Whilst there is strong evidence to suggest hunting and habitat fragmentation is a likely cause of extinctions, there is still much debate as to whether such practices were a result of changing climatic conditions. In later blogs I will discuss how the extinction process is even more complex, suggesting other possible factors explaining the decline of mega fauna in the late Pleistocene.
When our early ancestors entered new lands they encountered a variety of strange new creatures..... Enjoy!
Johnson, C.N., 2006. Australia's Mammal Extinctions: A 50 000 Year History. Cambridge University Press, Melbourne.